Review of the Prior Art
Loudspeaker enclosures designed for reproducing relatively low audio frequencies, i.e., in the range from about 100 hertz and below, have long been subject to objectionable resonances within the frequency ranges of their operation. For the purposes of this invention, a bass or low frequency loudspeaker or loudspeaker enclosure, is one intended to reproduce sound in the range of from about 250 hz and below down to the lower limit of the human hearing range which is in the neighborhood of 15-25 hz., depending upon the individual.
The problem encountered with a typical bass loudspeaker and its enclosure is that the combination tends to resonate at one or more points in the frequency range in which it is operated. These resonances result in boominess of the speaker, which boominess is sometimes preferred but which, nevertheless, is not consistent with faithful reproduction of the sound intended. For example, a typical bass loudspeaker enclosure is used to reproduce music in combination with mid-range and high frequency loudspeakers and enclosures therefor, in either a home or commercial audio system. In such a system the sound is recorded either on a phonograph record or on magnetic tape. The lower frequency sounds, as heard by a user of the system, are accentuated at some frequencies as compared to the relative volume of the sounds for those frequencies as recorded on the record or tape.
Great care is taken in the modern recording industry to cause the sound recorded on a phonograph record or tape to correspond, in frequency and volume, as faithfully as possible to the sound of the performance reproduced in the recording. Similarly, modern electronic audio equipment (amplifiers and the like) are extremely linear over their operating ranges and faithfully amplify and present to the loudspeakers electrical signals which similarly faithfully correspond to the sound generated in the performance embodied in the phongraph or tape recording. The presence of resonances in the loudspeaker system used to transduce the electrical output of the audio amplifier to an audible signal is at odds with and subverts the care taken in the original recording and in the reproduction amplifiers. These resonances are due in part to resonance effects in loudspeakers, but more importantly, as I have discovered, to resonances within the loudspeaker enclosures themselves. I have found that low frequency loudspeakers are very similar to each other in overall performance characteristics in respect to resonances, and that the more expensive low frequency loudspeakers now commercially available show only a small improvement in resonance characteristics as compared to the lower priced low frequency speakers commercially available.
That is, in the combination of a low frequency loudspeaker and an enclosure therefor, I have identified the enclosure, rather than the loudspeaker, as the principal source of resonances in the range of audible sound which the loudspeaker is used to reproduce in an overall audio reproduction system. A need therefore exists for an improved loudspeaker enclosure which, when used in combination with a low frequency loudspeaker, reproduces sound over the intended frequency range without objectionable resonances at one or more frequencies within such range.